Currently over 100 biological products are produced using recombinant technology wherein bacterial or mammalian DNA is modified to direct host cells to express and/or secrete proteins of interest. In the future, it is anticipated that more than three-fourth of all new drugs will be biologics, including drugs expressed using recombinant host cells cultured in bioreactors.
When using host mammalian cells, which represents the most significant cell used in recombinant drug expression for the manufacturing process, the standard upstream unit operations involves culturing recombinant host cells in a bioreactor under conditions which promote the expression and secretion of the target biological proteins into the culture media.
The current trend for cell culture processes is to increase product titer through using enriched culture media, or longer periods of culture duration. However, the increased cell mass and improved cell productivity, is usually accompanied by decreased levels of cell viability, and an increased likelihood that the target biologic will be exposed to unfavorable environmental conditions attributed to increased levels of process impurities (e.g. such as host cell proteins, nucleic acids, lipids, colloids) present in the cell culture media.
Typically, the first upstream unit operations involve separating the mammalian cells from the culture media at the end of the cycle (e.g., by centrifugation, precipitation and/or filtration) and reducing the media volume by ultrafiltration in order to prepare the biological protein for subsequent downstream processing using a series of unit operations designed to purify the target protein from undesirable culture by-products, host cell proteins and process related impurities or contaminants.
It has been estimated that downstream processing accounts for 50% to 80% of the total manufacturing cost of a therapeutic antibody. The purification unit operations of a typical protein manufacturing process routinely involve a capture step and at least one, and typically more than one, polishing step. It is well known that the standard unit operations used to manufacture biological products are characterized by disadvantages resulting from the use of cell separation techniques that require the use of high G-force centrifugation, or shear forces that can negatively impact host cell integrity, as well as the quality of the biological product.
For example, the use of an ultrafiltration step to concentrate the drug substance at the end of the upstream unit operations can result in lower yields or poor quality product that is more likely to exhibit inconsistency in its structure. Additionally, the cost of equipment, the long process times and the validation of cleaning required for GMP manufacturing can make the traditional process extremely cumbersome, inefficient and expensive.
In addition to the concerns discussed above, there can also be issues with the effect of spent cell culture media on the viability of the host cell and/or the quality of the expressed biological target protein. Many metabolites and by-products (e.g., host cell proteases) released during high cellular density culture conditions can be detrimental to the stability and quality of a targeted biological product. Some of these concerns can be minimized by using a perfusion-based culture system in which the culture media is constantly refreshed by the addition of fresh culture media, the high cost of cell culture media (ranging from less than $5/L for bacterial culture to over $100/L for mammalian culture) makes this option extremely expensive. In addition, depending on the scale of the manufacturing operation, perfusion or fed batch culture methods can be a cumbersome and time consuming process.
Therefore, there is an unmet need for robust manufacturing methods that are streamlined to reduce the cost, and increase the efficiency of processes used to manufacture biological products. Ideally, an optimized manufacturing process should reduce the level of stress the target biologic product is exposed to, improve the efficiency of the process and reduce the costs by combining or reducing some of the unit operations that are routinely used in established protocols.